Process and system for rotary drilling with drilling fluid imposed sonic vibrations



Apnl 21, 1970 l. BASGAN 3,507,341

PROCESS AND SYSTEM FOR ROTAR Y DRILLING WITH DRILLING FLUID IMPOSED SONIC VIBRATIONS Filed June 24, 1969 4 K I 8 5 9 13 5 G 7 16 10 j H F I 'l ,14 H 1 f L INVENTOR m ION BASG-AN 4 BY a a. I 41 5 M, I (fl n/ ATTORNEY United States Patent 3,507,341 PROCESS AND SYSTEM FOR ROTARY DRILL- ING WITH DRILLING FLUID IMPOSED SONIC VIBRATIONS Ion Basgan, 4 Cernica, Bucharest, Rumania Continuation-impart of application Ser. No. 645,227, June 12, 1967. This application June 24, 1969, Ser. No. 836,058

Int. Cl. E21b 3/00, 21/00 U.S. Cl. 17556 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a system and apparatus for drilling earth formations and to a method operating the same, the apparatus comprising a rotary drill string composed of an upper pipe section and of a lower tubular drill collar and of a bit fixed to the lower end of the drill collar, means including a hoist for suspending said rotary drill string from a derrick, and means for feeding the drilL ing mud to the top end of the drill string causing the latter to be immersed in the mud filling the bore hole. By means of the hoist the drill string is so suspended in the derrick that the Weight acting on the bit is limited to a low force of, for instance, 2 t. In the novel system the weight of the drill collar is from 10 to 50 percent greater than the weight of the liquid volume of mud displaced by the drill collar and by the drill pipe plus the maximum weight acting on the bit in operation. When the bit is subjected to percussions, the vibratory energy transmitted into the liquid flow and the drilling string by longitudinal waves is produced at the upper end of the drilling string. Moreover the exciting force which generates the longitudinal vibrations or percussions, measured at the swivel, is from 10 to 30 percent greater than the weight acting on the bit in operation and an increase of the mechanical drilling speed is obtained through an increase of this exciting force produced by pressure variation of the liquid mud flowing into the upper end of the drilling string.

The vibratory energy is created by a pumping apparatus producing a fluctuating discharge pressure having an adjustable frequency. Control is facilitated by control instruments such as a pressure gauge, a frequency meter and a pressure and frequency variation recorder. The frequency is so chosen that resonance is obtained between the frequency of the fluctuating discharge pressure and the natural frequency of the longitudinal oscillations set up in the drill string. As a result of this resonance the longitudinal vibrations may be made so powerful as to lift the bit off the bottom of the hole.

CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of now abandoned application Ser. No. 645,227 filed June 12, 1967 forBig Drillers of Sonic Frequency Rotary and Rotar-Percussion Types as well as the Relevant Apparatus.

BACKGROUND OF THE INVENTION Field of the invention Method and apparatus for roto-percussive drilling in the ground while imparting vibrations to the column of drilling mud that flows down the conduit formed by the drilling string.

Description of the prior art The drilling methods known and used today are of the hydraulic rotary type using a drilling string consisting of a bit, a drill collar, drill pipes, a kelly and a swivel. The mud circuit which transports the drilled material to the surface is actuated by mud pumps. The bit is advanced by rotation and by the mud flow and the weight on the bit. The drill collar is so designed that its Weight exceeds the weight acting on the bit by about 30 percent, the weight of the bit amounting to about .75 of the weight of the drill collar. It is to be understood, of course, that the drill collar is composed of sections screwed together so as to function as a unit, each section having a length of about 30 ft., the total weight of the drill collar depending on the number of such interconnected sections. The weight acting on the bit equals the weight of the drill string including the drill collar minus the weight of the displaced mud minus the supporting force exerted by the hoist in the derrick on the drill string. The hoist is so adjusted as to obtain the desired weight acting on the bit.

In United States Patent No. 2,103,137 there is shown a hydraulic rotary drilling apparatus provided with a piston pump for mud circulation, in which the drilling string includes drill collars of weight G calculated by the formula G =K G +K+P, where G is the drilling string weight, K is a coeflicient with values ranging from .15 to .20; K is the mud friction force through the bit nozzles, estimated at 50 kg. (which is a negligible figure compared with the other members of the equation), and P is the weight on the bit. As a result, the weight G is substantially equal to the sum of 1) the weight K 6 of the mud displaced in the bore hole by the drilling string and (2) the weight P which must act on the bit in operation for the proper drilling effect. Therefore, the entire length of the drill collar is subjected to compression by the hydraulic pressure acting on the bottom of the bit. This is a great disadvantage because the longitudinal waves transmitted to the upper end of the drilling string and propagated downwardly in the steel walls thereof will stop at the neutral zone between the section of the drilling string subjected to tension and the section subjected to compression. Hence, these waves will not enter the drillcollars and, therefore, cannot impart a substantial up and down movement thereto.

This prior patent disclosed a second piston connected to the liquid circuit, the two pumps creating longitudinal vibrations in the liquid column and in the drilling string simultaneously with the bit rotation. This earlier invention introduced into the hydraulic drilling technique, rotopercussion with a sonic frequency oscillator, effectuated in the liquid circuit and transmitted to the bit through the cleaning fluid (mud) and the drilling string.

With the aforesaid rote-percussive hydraulic drilling method improvements were proposed such as using bottom vibrators with complicated parts placed in the bore hole above the bit; however, this did not succeed in realizing eflicient drillings and increased drilling depths; the same thing happened when using mechanical vibrators placed at the surface on top of the drilling string. The vibrators had complicated parts and adjustments which have not allowed, despite precautions taken to secure the resonance,

to obtain efiicient percussions at the bit.

The drilling methods known today, present shortcomings due to the frequent failures of bits, drill collars, and drill pipe, hole deviations, low drilling indices, costly operations and the relatively shallow depths can be reached.

SUMMARY OF THE INVENTION It is an object of the invention to provide a hydraulic rotary and roto-percussive vibration system of the character described which is a marked improvement over the prior art.

It is another object of the invention to provide a system of the character described in which the drilling indices and the mechanical and commercial drilling speeds are improved, the drilling indices being the variable parameters, such as the weight of the drill collar, the adjustnent of the hoist determining the weight acting on the 3H, the number of revolutions per minute etc.

It is another object of the invention to provide a sysem of the character described which realizes optimum lrilling conditions in formations of various hardnesses and which will obtain vertical bore holes even in very iteeply inclined strata.

It is another object of the invention to provide a sysiem of the character described in which hole accidents :uch as failure of drill pipes, drill collars and casings, :aving of key holes and excessive wear of drill pipes are :liminated.

It is another object of the invention to provide a sysem of the character described in which the depth and .hickness of different strata are precisely identified due to he fact that the bore hole is absolutely vertical.

It is another object of the invention to provide a sysem of the character described which creates favorable :onditions for drilling wells by ensuring a true vertical )rientation of the drilled bore hole.

It is another object of the invention to provide a sysem of the character described which substantially reluces drilling and producing costs.

It is another object of the invention to provide a sysem of the character described which permits the bore roles to be drilled to very great depths.

Other objects of the invention in part will be obvious and in part will be pointed out hereinafter.

The invention accordingly constitutes the features of :onstruction, combinations of elements, arrangements of arts and series of steps which will be exemplified in he hydraulic rotary and roto-percussive vibration system lereinafter described and of which the scope of applicaion will be indicated in the appended claims.

The present invention consists of a hydraulic rotary 1nd roto-percussive drilling system of suitable frequency, 1nd a corresponding apparatus constituted of a bit, a drill :ollar, drill pipes and swivel, respectively, as well as the means for suspending the drilling string from the derrick ind means for producing the vibration energy. The invenion removes the above mentioned shortcomings, without lsing underground complicated tools. At the bottom of he hole the liquid drilling mud is under a very high pres- .ure which, at a depth of, say, 5 miles, amounts to about 4,000 p.s.i. This pressure acts on the bottom of the bit 1nd exerts a very high pressure on the drilling string subecting the lower section thereof to compression. Above his section the drilling string up to its upper end is subected to tension by its weight. Both sections are divided )y a neutral zone in which the drilling string is subjected leither to tension nor to compression except for the negligible effect of any longitudinal oscillations that might 1e set up in the string. It is the essence of the invention hat the center of gravtiy of the lower section of the drillng string is lowered to a very low level by the use of a ery heavy drill collar, the weight of the drill collar being rom to 50 percent greater than the weight of the liquid plume of mud displaced by the drill collar and by the lrill pipe plus the maximum weight acting on the bit in 'peration. As a result, the drilling pipe section of the tring is kept entirely free from compression and, thereore, is not likely to be bent laterally as would be the ase with pipe subjected to compression. In fact, the neural zone is located below the upper end of the drill collar nus restricting the compression section of the drilling tring to the drill collar which owing to its comparatively lrge diameter is capable of resisting compression without ny lateral deflection. My novel drilling string constructed 1 accordance with this invention may have a drill collar f a length of 450 ft. with a depth of the bore of 6600 ft. )wing to the absence of any lateral deflection of the drillig string the hole will be bored in an absolutely vertical lirection.

It is common practice in drilling earth formations to withdraw the drilling string periodically, whenever the bit must be replaced and to couple in added length of drilling string. My invention requires that on such occasion added drill collar sections be coupled in for the purpose of maintaining the weight of the drill collar within the limits set forth hereinabove. Therefore, the length of the drill collar must be intermittently increased as the depth of the bore hole progresses.

A further advantage of the high weight of the drill defined hereinabove is the high momentum of rotation resulting in a more even rotary velocity of the drill collar irrespective of abrupt variations of the resistance encoun tered by the bit during its rotation.

Another advantage of the location of the neutral zone below the pipe section is an excellent transmission of the oscillating energy from the surface to the bit. The invention obtains an efficient infrasonic drilling regime, with an amplitude, frequency and a determined ratio between the force creating the infrasonic flow and the drilling pressure on the bottom, for oil exploitation and for reaching greater depths into the earth crust, by drilling vertical and economical bore holes that can reach and even go over the depth of 10 to 15 km.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings in which is shown one of the various possible embodiments of the invention the sole figure is a schematic representation of the system for effecting sonic or combined drilling methods with the corresponding drill collars and the sonic collector.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the hydraulic rotary drilling system according to this invention, the weight of the drill collars is increased progressively from the beginning of drilling, or as the hole is deepening, inasmuch as all the time during drilling, the total weight of the drill collars, accordingly denominated and noted as G shall be from 10 to 50 percent greater than the weight of the liquid volume G displaced by the drilling string immersed into the drilling liquid, plus the weight P on the bit. This can be expressed by the formula:

wherein x is not lower than 1.1 and not higher than 1.5.

For the purpose of explanation let us consider the drilling of a bore hole of a depth of 6667 ft. drilled with 5% inch drill pipes and 6% inch drill collars. The specific weight of the mud amounts to 1.2-1.8 kg./dm. The specific weight of the steel amounts to 7.8 kg./dm. In this case the pipe section of the drilling string is given a length of 6167 ft. and the length of the collar of the drilling string is given a length of 500 ft. The weight of the thin-walled pipe section amounts to 12.6- kg./ft. and the weight of the drill collar amounts to 60 kg./ft.

The weight G is calculated as follows:

As a result we obtain G =24 tons.

The weight P acting in operation of the example on the bit amounts to 2 tons. Therefore, the present invention requires that G is 1050 percent larger than 24-1-2 tons or 26 tons, e.g. 15 percent, which means that x equals 1.15. This result in 30 tons or, in other words, in an increase of G by 4 t. compared with the prior art value of 26 t. This increase by 4 t. results in lowering the neutral zone (which divides the compressed part of the drilling string from that under tension) by 66 ft. into the drill collars mass. (The process can also be applied to turbo-drilling. In this process the drilling string does not rotate. A turbine is mounted on its lower end and imparts rotation to the bit. Just as the turbine of a jet engine produces axial thrust, the turbine exerts a downwardly directed axial force on the drill string. Therefore, in this case the weight G of the drill collar should be reduced by this axial force.)

As explained hereinabove, the use of drill collars lowers the neutral zone by means of the prescribed drill collars weight within the drill collars length.

In this way the bore hole deviation is avoided and vertical boring results. Also, important advantages explained hereinabove are obtained, especially by increasing the well known commercial drilling speed.

The lower and closer to the bit the neutral zone is brought, the better will be ensured the vertical equilibrium of the drilling string and the bore hole, overcoming and limiting the effect of the Archimedean pressure and the lower will be the stresses set up in the material of the drilling string.

My novel hydraulic rotor-percussive drilling system comprises apparatus mounted on the ground near the well-head for producing the vibratory energy to be introduced into the well, such apparatus being equipped with means for determining the frequency of the vibration and the maximum and minimum pressures produced thereby in the liquid mud introduced into the swivel supporting the drilling string.

The apparatus is diagrammatically shown in the drawing. It comprises a container 7 communicating with one or two mud pumps 11, 12 and with means causing the pressure in the container 7 to fluctuate between a maximum and a minimum differing by the differential pressure P In the example shown such means comprises a cylinder formed in the instant embodiment by the end section of the tubular container 7 and a reciprocating piston operated by power-driven means such as a suitable infrasonic generator 13 which is so designed that both the frequency of reciprocation of the piston and the piston stroke are adjustable. As such infrasonic generators are well known in the art, a detailed description thereof may be dispensed with. The container 7 including the cylinder is hydraulically interposed in series between the pumps 11, 12 and the top of the drill string.

The container 7 communicates by a hose 6 with the swivel from which the drill string 2, 3, 4 is suspended. Moreover, the container 7 communicates with a pressure gauge 8, a pressure recorder 9 and a frequency meter 10.

The pumps 11 and 12 suck the mud from a sump 14 to which the mud is returned that is discharged from the well-head 15.

In the container 7 the liquid mud is subjected to a pressure that fluctuates at the desired frequency which, as a rule, is an infrasonic frequency, between a maximum value and a minimum value, the difference of these values amounting to a pressure P which is indicated by the gauge 8. The pumps 11 and 12 may be piston pumps and their speed is synchronized with the speed of the generator 13 by a suitable control apparatus diagram matically shown at 16, which is cooperatively associated with speed control means of the pumps and of the infrasonic generator 13 as diagrammatically indicated in the drawing by the lines connecting apparatus 16 with the pumps and with the infrasonic generator. The apparatus 16 permits to adjust the speed or frequency of the infrasonic generator and of the pumps within an infrasonic range. The fluctuating or vibrating pressure produced in the container 7 and the hose 6 acts with a force K on the cross-sectional area of the internal conduit of the drill string 4, such area being indicated by the arrow S. This force K acts upwardly and is vertical. It is produced by the internal pressure in the bowl with which the hose 6 communicates. This force K varies with the frequency of the generator 13 and with the stroke of its piston and subjects the drilling string to a longitudinal vibration propagated in the drilling string, i.e. through steel, at a velocity of about 5000 m./sec., to the bit.

The swivel 5 carrying the drill string and the bowl thereabove are suspended from the usual travelling block 20 and cable suspending in the derrick 21. The travelling block 20 forms part of a hoist which is so controlled in the conventional manner as to keep the weight P acting on the bit within the desired limits. As this is well known in the art, a more detailed description thereof may be dispensed with. Preferably, the stroke of the piston operated by the generator 13 and, consequently, the force K is so chosen in operation that it is higher than the force P. As a result, the bit is subjected to a vertical vibration or oscillation through a distance a. In other words, the bit rises and falls on the bore hole with the frequency n and with a stroke a. By means of the control apparatus 16 the frequency is so adjusted that resonance of the vibration in the string 2, 3, 4 is obtained. This condition is indicated by the increase of the vibration of the swivel 5 to a maximum and will be readily recognized by the operator.

The rotary drill string comprises (1) an upper section 17 composed of pipe 4, (2) a lower section 18 constituting the drill collar and (3) a bit 1 fixed to the lower end of section 18. The drill collar is composed of a multiplicty of rigidly interconnected tubular drill collar sections each section usually having a length of 50 ft. These interconnected drill collar sections act as a unit. The weight G of the lower string section 18 is so chosen as to be from 10 to 50 percent larger than the sum of G and P, G being the weight of the mud displaced in the bore hole by the drilling string and P being the weight which must act on the bit in operation for a proper drilling effect. The weight G prevents the hydraulic pressure exerted by the mud on the bottom of bit 1 from subjecting the upper section 17 and a top portion 19 of the lower section 18 to compression. N is the neutral zone at which the drill collars 2 subjected to compression join the drill collars 3 subjected to tension. The relative length of the top portion 19 depends on the coetficient x which amounts to from 1.1 to 1.5. The length of the top portion 19 can be easily calculated as was done hereinabove for the example dealing with a bore hole of a depth of 1667 ft. The vibratory waves set up in the steel walls of the pipe 4 and propagated downwardly therein cannot pass through the neutral zone N owing to the phenomenon of cavitation. However, they will safely reach the drill collars because of the location thereof above the neutral zone N. Therefore, these vibrations will impart a positive up and down motion to the drill collars 3 and in this motion drill collars 2 will participate owing to the stiffness of section 18 of the string thus moving the bit 1 positively up and down through the distance a.

It has been ascertained, pursuant to the present invention, that the force K should be in a certain ratio in relation to the weight P on the bit, namely preferably from 10 to 30 percent greater.

If the pressure maximums and minimums are and 20 kg./cm. respectively, then P =8020=60 kg./cm.

The pressure P acts upon the internal cross section S of the drilling string conduit. This relationship can be expressed by the formula:

If S=50 cm. and 60 kg./cm. then K=3000 kg. or 3 tons.

The relationship between K and P chosen in accordance with my invention is expressed by the equation wherein y amounts to a figure not smaller than 1.1 and not larger than 1.3. Taking y=1.3 and K=3 t. as an example, we obtain P=2.3 t. Therefore, the hoist including the traveling block 20 must be so adjusted that the weight acting on the bit 1 amounts to 2.3 t.

Hence, the drilling weight acting on the bit will be always maintained lower than 3000 kg. so that the vibratory pressure P creating the force K and propagated through the drilling string to the bit raises the latter rhythmically with the frequency n and with an amplitude a, this amplitude being an adjustable function of the difference K-P and of the frequency 11.

In this way the bit always falls on a true vertical gravity line thus drilling a vertical hole. The percussion will break the rock in front of the bit and the rotation and the fluid circulation will clean the drilled material, increasing the mechanical drilling speed.

In the case of roto-percussive drilling, the lowering of the neutral Zone avoids any adverse effect of the cavitation phenomenon in the drill pipes and allows the transmission of the vibratory energy to the bit, the bit falling on the bottom by following the direction of gravitation, a stable and balanced drilling string being used.

When a longitudinal oscillation is excited in the top portion of a drilling string transmitting longitudinal waves through the steel walls of the string downwardly to the bit, this transmission will be stopped by the neutral zone extending between the upper portion of the string subjected to tension and the lower section of the string subjected to compression. In other words the downwardly propagated waves will disappear at the neutral Zone. This is the cavitation phenomenon. As the neutral zone in my novel system is located well below the top portion of the string collar, the waves will positively reach such top portion and will thereby raise and lower the ;p portion of the collar. Because of the great strength at the collar, the lower portion thereof with the bit will participate in such up and down motion and act like a Jammer. This will explain why the vibratory operation )f the bit is considerably assisted by the use of a par- :icularly heavy collar as defined by the equation for 3 stated hereinabove.

The requirement of the roto-percussive drilling P y=K :stablished before means that the weight on the bit is smaller than the exciting vibration force K.

A compliance with this requirement is of great ad- Iantage irrespective of the magnitude of K. Where K :annot be increased beyond a comparatively low limit is is true with the drilling equipments in common use )rior to this invention, the efiiciency of the drilling :quipment will be considerably increased by making P smaller than K even though that means restricting P to in amount much smaller than customary heretofore.

My invention increases the life of the bit working on he bottom of the hole and, therefore, the footage per )it. By using my new percussive rigs which allows greater Ialues for the pressure variation P and the exciting libration force K, drilling can be carried out with valms for the weight on bit permissible at present at much iigher mechanical drilling speeds.

By using a drilling string made with presently availtble superior strength materials, and the new equipment iroposed in this invention, which lead to a greater value )f K and thus using an increased P wells can be drilled o depths increased up to -15 km.

The above stated established the drilling rig parameters Ll'ld the hydraulic roto-percussive drilling regime, with nfrasonic frequency.

My invention results in an increase of the commercial peed and of the mechanical drilling speed. In my novel ystem the exciting vibration force K, the pressure differ- :nce P of the pump output, and the internal cross secion of the drilling string is increased beyond the values ustomary heretofore.

The frequency n is so chosen as to obtain resonance lllWI1 the frequency adjusted by means of the appaatus 16 and the natural frequency of oscillation of the lrilling string. This can be achieved without exceeding he infrasonic frequency limit.

My novel drilling string complying with the requirenent (wherein x is 1.1 to 1.5) can be used without any vibration of the type y -P=K and will still achieve many of the advantages outlined hereinabove, such as the increased rotary momentum of the drill collar and the increase of the length 19 in which the drill collar is subjected to tension and, therefore, will not bend laterally. I prefer, however, to use my novel drilling string with the specific vibration imparting a positive up and down reciprocation to the bit. My novel drilling string can be used for Corning, pumping, fishing etc.

When the weight P on the bit 1 is maintained lower than the force K, the bit works under a percussive regime, the bit rising with an amplitude a and falling on the bore hole bottom with a frequency n.

It thus will be seen that there is provided a system which the several objects of the invention and which is well adapted to meet the conditions of practical use.

What I claim is:

1. In a system for drilling earth formations, a drilling string comprising an upper section composed of pipe, a lower section composed of a tubular drill collar rigidly fixed to said upper section and a bit attached to the lower end of said lower section, means mounted on the ground and fixed to the top end of the drilling string for suspending the drilling string and adjusting the weight P acting on the bit in operation, and means for feeding drilling mud to the top end of said drilling string causing the latter to be immersed in the mud filling the bore hole, the weight G of said lower section being from 10 to 50 percent larger than the sum of (1) the weight G of the mud displaced in the bore hole by said drilling string and (2) the weight P whereby the weight G prevents the hydraulic pressure exerted by the mud on the bottom of the bit from subjecting said upper section and a top portion of said lower section to compression.

2. The combination claimed in claim 1 further comprising hydraulic means connected to said upper section for supplying drilling mud to said pipe under pressure including means casing said pressure to fluctuate between a maximum and a minimum differing by the differential pressure P which when multiplied by the internal cross section of said drilling string results in a pressure K, the relationship between K and the weight P acting on the bit being expressed by equation P-y=K, y amounting to from 1.5 to 1.3, whereby the pressure K will lift and lower said bit owing to the longitudinal vibration set up in the metal of said drilling string and transmitted from said means downwardly through said upper section thereof to said top portion of said lower section both subjected to tension.

3. The combination claimed in claim 2 in which said means for feeding drilling mud to the top end of said drilling string comprises a cylinder communicating with the conduit of said top end of said drilling string, a piston guided for reciprocation within said cylinder, powerdriven means for reciprocating said piston with a frequency n, and means coordinated to said power-driven means for adjusting 12 within an infrasonic range.

4. The combination claimed in claim 3 further comprising an instrument coordinated to said cylinder for measuring and indicating the difference between the maximum pressure and the minimum pressure produced within said cylinder by said piston, and an instrument for measuring and indicating the frequency 11.

5. A process of operating a system for drilling earth formations of the type including a rotary drilling string comprising an upper section composed of pipe, a lower section composed of a tubular collar rigidly fixed to said upper section and a bit attached to the lower end of said lower section, means mounted on the ground and fixed to the top end of the drilling string for suspending the drilling string and adjusting the weight P acting on the bit in operation, means for feeding drilling mud to the top end of said drilling string causing the latter to be immersed in the mud filling the bore hole, the weight G of said lower section being from 10 to 50 percent larger than the sum of (1) the weight G of the mud displaced in the bore hole by said drilling string and (2) the weight P, which process comprises the feeding of said drilling mud with a pressure fluctuating between a minimum and a maximum differing by the differential pressure P and raising said differential pressure to a figure whose product K with the internal cross section of said top end of said drilling string is related to said weight P in accordance with the equation P-y=K wherein y amounts to form 1.1 to 1.3.

6. In a system for drilling earth formations, a drilling string comprising an upper section composed of pipe, a lower section composed of a tubular drill collar rigidly fixed to said upper section and a bit attached to the lower end of said lower section, means mounted on the ground and fixed to the top end of the drilling string for suspending the drilling string and adjusting the weight P acting on the bit in operation, means for feeding drilling mud to the top end of said drilling string causing the latter to be immersed in the mud filling the bore hole, and hydraulic means connected to said upper section for supplying drilling mud to said pipe under pressure including means causing said pressure to fluctuate between a maximum and a minimum differing by the differential pressure P which when multiplied by the internal cross section of said drilling string results in a pressure K, the relationship between K and the weight P acting on the bit being expressed by equation P-y K, y amounting to from 1.5 to 1.3, whereby the pressure K will lift and lower said bit owing to the longitudinal vibration set up in the metal of said drilling string and transmitted from said means downwardly through said upper section thereof to said top portion of said lower section both subjected to tension.

References Cited UNITED STATES PATENTS 2,103,137 12/1937 Basgan 17556 3,405,770 10/1968 Galle et al. l7556 ERNEST R. PURSER, Primary Examiner US. Cl. X.R. l7357; 175-65 

